1. Field of the Invention
The present invention is directed to an interferometer with a single-mode optical waveguide wound in a coil which waveguide has a surface at each end for accepting light into the waveguide and for displaying light traveling in the waveguide.
2. Prior Art
Interferometers, which utilize a single-mode waveguide such as a fiber wound in a coil are known and described in an article by V. Vali, R. W. Shorthill and M. F. Berg, "Fresnel-Fizeau Effect in a Rotating Optical Fiber Ring Interferometer," Applied Optics, Vol. 16, No. 10, October 1977, pp. 2605-2607. These interferometers can be applied with the explanation of the Sagnac-effect for the measurement of angular velocities. To that end, linearly polarized light is coupled into the waveguide by its acceptance surface so that light travels in the guide in both directions. By means of superimposing the light emerging from the two ends or display surfaces of the fiber, an interference pattern can be generated whose proportional intensity distribution produces information concerning the movement state of the coil relative to an inertial system. The positional distribution of the light intensity is a function of the mutual phase amplitude of the light rays emerging from the light display or end surfaces of the waveguide. If the coil is at rest with respect to the inertial system, then the transit time of the two light beams traveling in the fiber in opposite directions are exactly equal since no non-reciprocal effects occur in the waveguide. If the coil turns in relation to the inertial system, then because of the relative Sagnac-effect, which is explained by an article by E. J. Post, "Sagnac Effect," Reviews of Modern Physics, Vol. 39, No. 2, April 1967, pp. 475-493, a transit time difference, which is different from zero, occurs and the phase amplitude of the light beams emerging from the display surfaces of the fiber are no longer the same. By evaluating the positional intensity distribution in the superposition range of the light beams, rotational velocity of the coil can be determined. Single-mode waveguides are used because a straight forward light path is provided therein. A single-mode waveguide is understood to be a waveguide which conducts or can only conduct a single mode of light.
In such interferometers, the problem occurs that the single-mode waveguide in general alters the polarization state of the beam of light in an unpredictable manner. Therefore, a complete interference of the superimposing light beams is prevented.